1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine and a printer, and more specifically, to an air-blow sheet feed device used therein.
2. Description of the Background
Image forming apparatuses are used as copiers, printers, facsimile machines, and multi-functional devices combining several of the foregoing capabilities. For such image forming apparatuses or sheet conveying devices used therein, various sheet feed devices using air separation instead of frictional separation have been proposed to enhance sheet-separation performance with various different types of sheets.
For example, a conventional sheet feed device has a sheet press member that enables separation air blown from one side of the device to pass through the device to the opposite side.
Another conventional sheet feed device has a member for opening and closing an air passage near a point at which an air knife contacts loaded sheets, thus allowing the thickness of the air knife contacting the loaded sheets to be sequentially changed.
In still another conventional sheet feed device, blowing air is directed downward to an upper face of a sheet.
In further still another conventional sheet feed device, the shape of an air-blow nozzle is selectable or replaceable in accordance with sheet characteristics to separate various types of sheets, which range from thin paper to cardboard, having different properties.
However, such sheet-feed separating systems using air flow may depend largely on factors associated with sheet shape, such as elasticity and deflection. Although various improvements in nozzle shape or air blowing angle have been attempted, it is difficult to provide a quantitatively assured separation quality since its manufacturing process depends largely on manual operations.
When a compressor is used in such sheet-feed device, increases in power consumption and noise may need to be improved.
Furthermore, the adhesion force between sheets cannot be defined by only the friction coefficient between sheets. For example, the sheet adhesion force falls into a mechanical adhesion force due to burrs generated in cutting, a tacky adhesion force generated by changes in surface coat layers due to changes in temperature and humidity, and an electrostatic adhesion force as generated in an OHP (overhead projector) sheet.
Then, as the capacity of a sheet feed tray in such sheet feed device is increased, lower sheets receive more weight of upper sheets. As a result, the adhesion force between sheets is increased, thereby lowering the sheet-feed separation performance.
Other conventional sheet-feed mechanisms have been proposed in which a member for assisting the sheet separation function of a sheet-feed separation unit with airflow is separately provided independent of the sheet-feed separation unit. Although various improvements have been attempted on such mechanisms, a recent increase in sheet types may pose challenges for the reliability of such sheet-feed mechanisms.